Purpose : To evaluate the efficacy of multislice computerized tomography (MSCT) in imaging the upper and lower limb arterial tree in trauma, peripheral vascular disease and bone tumors. Materials and methods: Since the installation of multidetector CT (4 detectors) in our institution, 35 patients have undergone CT angiography of the upper or the lower limb. Of these, 23 were of suspected arterial injury, 10 were with symptoms of peripheral vascular disease and 2 patients had a bone tumor. All patients were scanned in the supine position with a slice thickness of 3 mm and a collimation of 2.5 mm in a single sitting, with 150-180 cc of water based iodinated contrast medium injected at a rate of 3 cc/sec, via a pressure injector. Axial images were then reconstructed with 50 percent overlap and then transferred to a dedicated workstation for 3-D reconstruction and analysis; in maximum intensity projection (MIP), volume rendered (VR) and surface shaded display (SSD) images. The findings were then retrospectively compared with the surgical outcome in cases of trauma with suspected arterial injuries; or Colour Doppler correlation was obtained, for patients of peripheral vascular disease. Results : All the patients withstood the procedure well, with diagnostically adequate vascular enhancement. No image degradation due to respiration or motion artifacts and no serious post procedure complications due to the amount of contrast or the radiation dosage used were noted. CT angiography allowed a comprehensive diagnostic workup in all trauma cases with suspected arterial injuries, showing spasm in 7 patients (30.43 percent), compression in 9 patients (39.13 percent), contusion in 4 patients (17.39 percent) while any vascular injury was positively ruled out in 3 patients (13.04 percent), thus aiding in their management in a critically significant short time. The bony skeleton, soft tissues and the other visceral organs were simultaneously evaluated for the presence of any injury. In the 10 cases of peripheral vascular diseases, CT angiography adequately demonstrated the presence of any stenosis or occlusion, its degree and extent, the presence of collaterals and distal reformation if any; the presence of plaques, soft or calcified and the probable usefulness and the type of treatment, which should be employed. The role of CT angiography in the evaluation of bone and soft tissue tumours could not be fully explored due to inadequate number of cases. Conclusion : Our initial experience of CT angiography with multislice CT has clearly demonstrated its efficacy as a promising new, fast, accurate, safe and non-invasive imaging modality of choice in cases of trauma with suspected arterial injuries; and as a useful screening modality in cases of peripheral vascular diseases for diagnosis, for grading, for potential usefulness and type of treatment and also in the follow-up of patients, post treatment.

The availability of the "state of art" technology of multislice CT scanner (MSCT) has revolutionized the evaluation of peripheral vasculature in our institution, especially in trauma cases. As we are a large trauma center, this has made a significant impact in the diagnosis and treatment of such cases. It is indeed a beginning of a new and exciting journey and our initial experience of 35 patients in the last ten months has successfully guided the surgeon's knife with a correlating outcome.

Evaluation of peripheral vasculature is an integral part in the management of patients with peripheral vascular disease, polytrauma patients with suspected vascular injury and in patients with bone and soft tissue tumors. The traditional means of evaluating vascular anatomy with conventional angiography was slowly replaced by digital subtraction angiography (DSA). Although considered as a gold standard in the evaluation of peripheral vessels, especially peripheral vascular disease, the role of DSA has now been challenged by recent advances in technology like colour Doppler, CTAngiography (CTA) and contrast enhanced magnetic resonance angiography (MRA). [7]

Though not considered a primary vascular imaging modality till a few years ago, CTA has experienced a technological quantum leap with the introduction of MSCT and has gained widespread acceptance in the imaging of the aorta, carotid, renal and iliac vessels.1, 3, 5, 8, 9 The introduction of multiple detectors with isotropic imaging capabilities has enabled CTA to surpass even MRA with regard to spatial resolution.[11]

We present our initial experience of MSCT in the evaluation of peripheral vasculature. Our MSCT, Somatom Plus 4 Volume zoom (Siemens, Erlanger, Germany) can capture four slices of data in a single gantry rotation. This allows for a dramatic increase in speed as well as linear coverage, thinner sections of entire anatomic territories; and at the same time eliminates misregistration and respiratory artifacts, thereby achieving volumetric imaging.[3]

Materials and methods

From July 2002 to April 2003, 35 patients had undergone peripheral CTA, of whom 23 patients had a history of trauma, 10 patients had suspected PVD while the remaining 2 patients had come for evaluation of bone tumors. Of these 35 patients, 28 patients were male and 7 were female, in a wide age group ranging from 4 years to 70 years. 27 patients had come for lower limb CTA and the remaining 8 for upper limb CTA.

Technique

All patients were scanned on a Siemens Somatom Plus 4 Volume Zoom CT scanner, in a supine position with head first for upper limb (UL) and feet first for lower limb (LL) CTA. The scan direction was craniocaudal for LL CTA, with the range from the level of infrarenal aorta to the pedal arch; while for UL CTA; the scan direction was caudocranial from the level of aortic arch to the palmer arch. The topogram length was adjusted to 1024mm(or more for tall patients). 150-180 cc of water based iodinated contrast medium was injected at the rate of 3cc/sec via a pressure injector through a 16-18 G angiocath, under a pressure of 300 PSI. The patients were instructed to continue quiet breathing for the duration of scan. The images were acquired with a slice thickness of 3mm and a collimation of 2.5mm, with a pitch of 1.5-2. The scan time varied from 25-30 sec for upper limb CTA and 35-40 sec for lower limb CTA.

The success of any CTA depends on the calculation of an accurate delay to start the acquisition of images after the injection of contrast, to get optimum arterial enhancement, not contaminated by the venous phase. In our study, the optimum delay was calculated by automated bolus tracking technique in 30 patients, wherein the machine automatically starts scanning once the level of contrast enhancement in the artery (aorta) reaches a preset value of 65-70 HU; while empiric delay of 15-17 sec was used in 2 upper limb CTA studies. In 3 patients with suspected compromise in cardiac ejection fraction, the delay was calculated by using the test bolus technique.

The images thus acquired were then processed in 180 degrees algorithm with 50 % overlap, thereby generating an average of 800-1000 images per study. The images were then transferred to a dedicated online workstation for display in various 3-D techniques like maximum intensity projection (MIP), surface shaded display (SSD) and volume rendered images (VR), [Figure - 1]. Although from the radiological point of view, the axial images were sufficient for diagnosis, the operating surgeons and referring physicians preferred the 3-D images. In addition to film interpretation, a soft copy review of CTA on either a dedicated 3-D workstation or PC based review station was often performed. Because of the size of generated dataset, considerable time was required for image reconstruction, (taking approximately one to two hours) and this remained a major limitation of the current technique.[6]

Results

In all of our initial 35 patients, there has been no technical failure. The procedure has been well tolerated and in no study was there image degradation due to motion artifacts. In 4 patients, there were artifacts from orthopedic implants, but in no way did it interfere with the diagnostic interpretation of the study.

Of the 35 patients, 23 had a history of trauma, of which 17 had lower limb injuries and 6 upper limb injuries. The findings are as given in [Table - 1]: -

The CT angiography was normal in 3 patients (13.04%). An obvious vessel contusion was seen in 4 patients (17.39%), with resultant complete block and failure of opacification of the distal vessels. In 9 patients (40.9%), there was compression of the vessel seen due to fracture segment pressing on the vessel (n=3), due to mass effect from the surrounding soft tissue edema or hematoma (n=4) or due to presence of traumatic pseudoaneurysm (n=2). The distal vessels were opacified, showing either normal or reduced caliber of the vessels. Of the 23 patients, 7 cases (30.43%) showed diffuse narrowing of the vessels that explained a clinically impalpable pulse.

All the patients with normal CT angiographic study or with the diagnosis of spasm were conserved and on follow-up, showed normal clinical examination. The patients of vascular compression, due to mass effect either from surrounding soft tissue hematoma, pseudoaneurysm or by fracture segments were explored and operated for removal of the cause of compression. All the three patients who had a complete block due to vessel contusion, had to undergo below knee amputation, as the limbs were nonsalvagable.

Thus all the trauma cases had a near cent percent clinical and per-operative correlation thus confirming our CTA findings. MIP images of a LL and UL trauma are given in [Figure - 2], [Figure - 3] and [Figure - 4] respectively.

Ten patients of peripheral vascular disease, with symptoms of decreased or absent pulses, claudication or rest pain also underwent CTA.

Seven of these patients had lower limb symptoms, while three patients had upper limb symptoms. Four of the patients had a history of diabetes mellitus, while two of them were hypertensive. Two of the three suspected upper limb vascular disease patients were found to be normal [Figure - 7], while one patient with lower limb symptoms was seen to be normal.

Each patient yielded two sets of arteries thus giving us a total of fourteen lower limb and six upper limb arteries. All the vessels were examined in the axial as well as the reconstructed views and classified into five categories, as normal, Grade I as <49% stenosis, Grade II as 50-74% stenosis, Grade III as 75-99% stenosis and complete occlusion.5

Both set of arteries were evaluated simultaneously and showed the transit time of contrast material to be identical on both sides. Vascular enhancement was excellent (>160 HU) in all cases. Useful additional information was simultaneously obtained in most of the positive cases. Adequate collateral formation was seen in four cases, while a positive diagnosis of plaques (both soft and calcified) was made in three cases and an obstructing thrombus seen in one patient. Apart from the three normal cases, the remainder of the positive cases was found to be due to atherosclerotic vascular disease [Figure - 6].

CTA was also performed in two known cases of bone tumors. One was a case of a subchondral Giant cell tumour, who on CTA showed intense vascularity of the lesion, hypertrophy of the superficial femoral and popliteal artery and presence of early draining veins [Figure - 5]. Another case that underwent CTA had a small cell tumor of the right tibia, which was seen to be completely avascular. Apart from this information which can also be obtained with conventional angiography, additional information was obtained as regards to the exact anatomical site of the tumor, it's extent, periosteal reaction, any cortical break or irregularity and associated soft tissue invasion, if any. These findings help to determine the aggressive nature of the tumor and in it's staging, as well as in surgical planning by showing its proximity to the surrounding major vessels and other anatomic landmarks.

Discussion

With the introduction of multiple detectors and resultant multiplanar imaging capabilities, CT angiography (CTA) has emerged as the leading modality in peripheral vascular evaluation.[11]

Of the 23 patients with suspected peripheral vascular injury, MSCT has been able to successfully demonstrate the abnormality within few minutes and with 100% operative correlation.[10] The peripheral arteries were affected either by dislocated bone fragments or by crush injuries and compression and mass effect from surrounding hematoma in 9 patients, in 7 patients, a clinically absent pulse was demonstrated due to severe spasm and vessel contusion was seen in four cases. Suspected vascular injury was ruled out in the remaining 3 patients. Thus MSCT helped in a comprehensive diagnostic workup of trauma patients within a critically short time. Moreover associated bone fractures, soft tissue injury and injury of other visceral organs were demonstrated in the same sitting. Immediate surgical repair was thus possible in life threatening cases.[10],[4]

In the evaluation of patients with bone tumors, CTA has a role in demonstrating the relation of the bone tumor to the major vessels, the presence of neovascularity within the lesion and the possibility of vascular invasion or involvement by the malignancy. It thus guides the surgeon regarding the operative technique (limited or wide excision) and the probability of successful outcome of the treatment.

The aim of CTA in peripheral vascular disease (PVD) patients is to delineate the presence or absence of significant obstruction to blood flow, the site and anatomical extent of obstruction, the status of collateral flow and distal vasculature; for planning treatment as well as to monitor the results of therapy and disease progression.[1], [7] The cause of peripheral vascular disease in all our positive seven patients was seen to be atherosclerosis. Other rarer causes of peripheral vascular disease like vascular aneurysms, cystic adventitial disease or popliteal entrapment syndrome were not seen in any of the cases.[2] CT Angiography is seen to have more than 92% sensitivity, 96.2% specificity and an overall accuracy of more than 95.5% in the evaluation of peripheral vascular disease.1 In all our PVD patients, CTA was successful in establishing the exact location and extent of the block, the collaterals and distal reformation, as correlated by colour Doppler studies. The advantage of CTA in cases of PVD is in the detection and characterization of atherosclerotic plaques and the presence or absence of calcification within it. This is significant, as in, the plaque morphology being heterogenous, some are more prone to calcify, while soft plaques are the potentially dangerous ones, due to their propensity to rupture and throw life-threatening emboli. In addition, by being able to more clearly define a plaque and its morphology, the effect of various therapies on progression or regression of plaques can be monitored.[11] However the presence of very heavy calcification is a disadvantage for CTA, as the vessels are then not adequately evaluated due to volume averaging artifacts, especially in smaller caliber vessels, beyond the level of the inguinal ligament.[6] However with the development of newer software logarithms, this drawback would be very soon overcome[1],[6]. The additional benefit of cross-sectional CT in simultaneously depicting extraluminal structures causing arterial obstruction, as in popliteal artery entrapment or cystic adventitial disease cannot be overemphasized.[2], [7] The major disadvantage of CTA however is the radiation dose and the absence of any hemodynamic assessment, which is obtained by Doppler imaging and MRA. In spite of these limitations, CTA is being increasingly used as a screening modality for initial assessment of the presence of vascular disease, its extent and severity, thereby allowing interventional radiologists and vascular surgeons to plan the most appropriate therapeutic method, reducing unnecessary intervention or possible intra-operative difficulty.

Thus it is easy to see why CTA has such tremendous growth prospects as a distinct diagnostic imaging modality in recent years. Apart from the fact that the radiation dose is four times less in CTA as compared to DSA, it is faster, non-invasive and combines luminal information provided by conventional angiography with the advantages of cross-sectional CT imaging.[2] The visualization of the wall of the vessels (calcified and soft plaques), along with a simultaneous evaluation of bone and soft tissues and the anatomic relationships of the vessels with adjacent structures is clearly a strength of CTA that cannot be matched by conventional angiography.[11]

Colour Doppler is the initial imaging modality of choice in suspected peripheral vascular disease, especially in popliteal disease, but it has a few drawbacks. It is operator dependent, is unable to assess distal vasculature and fails to demonstrate direct evidence of cystic adventitial or popliteal entrapment syndrome.[2] As against colour Doppler, CTA is less operator dependent and is clearly of advantage in patients with trauma that are often immobilized and in intense pain. Surgeons prefer CT images to Doppler images as they are presented in a format similar to conventional angiograms with which they are more familiar and comfortable.[6]

The main competitor to multislice CTA is contrast enhanced dynamic MRA. Both modalities have similar Z-axis resolution, however, MRA has an advantage by the fact that it is unaffected by the presence of vascular calcification.[6] In addition, MRA is a good imaging modality for evaluation of the distal anterior tibial, peroneal and dorsalis pedis arteries. However, CTA scores over MRA by being much faster, less expensive, more widely available, with better patient compliance and with the absence of retrograde flow artifacts. It is also a modality of choice in patients with MR incompatible hardware, indwelling stents and in severely claustrophobic patients.[7], [3]

In our study, the presence of joint prosthesis was a common factor in many patients, especially in trauma cases who had orthopedic implants. However, the fear of it throwing artifacts and degrading the image quality was proved wrong, in fact MSCT gave excellent diagnostic images even in the presence of metal prosthesis, indicating that the new generation of CT scanners are better able to cope with even severe beam hardening artifacts.

The major drawback of CTA is the large amount of intravenous contrast and the ionizing radiation involved. Also, no information is obtained regarding the flow direction and velocity. In addition, CTA may fail to demonstrate short segment stenosis, apart from the fact that horizontally oriented branches are poorly visualized, thus significant lesions may be missed in certain instances.[6]

Despite these limitations, the vast majority of examinations we performed were considered sufficiently diagnostic to avoid more invasive imaging.

Conclusion

Our initial experience of CTangiography with MSCT has shown that it is a promising new, fast, accurate and non-invasive imaging modality that can be utilized effectively in the evaluation of peripheral vasculature. It has given near 100% intra-operative correlation in patients of trauma and correlating confirmatory Doppler findings in patients of peripheral vascular disease. The contrast and radiation dose was well tolerated by all the patients and the image quality obtained was comparable to intra-arterial DSA. Some of the inherent limitations of the technique and the time consumed in post-processing can be overcome with future workstation and technology advances. Thus it would be appropriate to conclude that CTA is clearly emerging as a screening tool in patients of peripheral vascular disease, while in trauma patients with suspected vascular injury, it is the imaging modality of choice.